Dynamic properties of bearing bushes' support constructions are very important data in rotor-bearings systems' dynamic responses' modelling. The problems of assigning those properties is especially significant if the results of dynamic computations have to be used in simulation diagnostics of the rotating machinery (e.g. turbines, compressors etc.). It is known, dynamic stiffness, damping and mass coefficients are depended on force frequencies. So, if we assign constant values of those characteristics (e.g. obtained from the static test) in the whole frequency range, results of our computations may be inadequate to results of an experiment. Computer program called NLDW is created in IFFM PASci. In Gdańsk, Poland. It provides to simulate rotor dynamics with nonlinear methods. It needs dynamic characteristics of the bearing support to be real and non-negative numbers. The only research method to use in this case is a harmonic force response method giving complex flexibility and phase characteristics. So we have to transform them to real mass, stiffness and damping characteristics. In our opinion it is the most convenient to divide the whole frequency range into a number of so called "adequacy ranges" and make the transformation based on them. The characteristics are constant in those ranges. The main problem in this method is to find particular adequacy ranges limits (frequencies) making the transformation the most effective. The paper proposes to obtain dynamic characteristics of bearing bushes' support in a way of harmonic force response method and transform them in "adequacy ranges". Laboratory rotor stand and the bearing bushes' support frame are presented and the frame FE-model as well. Modal analysis is done in a range from 0 to 125 Hz. The theory of dynamic characteristics obtaining and transforming is briefly shown. In our opinion the way to divide the whole frequency range should be based on the modal analysis (resonant and antiresonant frequencies). It is possible to modify such kind of division to reduce all or particular ranges width. The result of analysis are presented and veryfied for a kind of division based on the modal analysis and modified in a way to make all ranges not wider than 20 Hz.